Permeable solar control film

ABSTRACT

The present invention provides an improved method for making a solar control sheet having one or more metal layers. In the prior art solar control sheets, each metal layer would normally be non-porous so that water vapor would not be readily transmitted therethrough. However, in this invention the metal layer is rendered porous because it is deposited on a porosity inducing surface. The porosity inducing surface may be the surface of a porous primer layer or a surface which has been roughened. Consequently when the solar control film of this invention is mounted on a window with a water based mounting media, the water can quickly evaporate through the film without causing undesirable cloudiness which is normally associated with water which becomes trapped between the film and the window.

This application is a Division of nonprovisional application Ser. No.08/586,312 filed Jan. 17, 1996, now U.S. Pat. No. 5,902,634.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to flexible energy control sheets andassemblies which include at least one optical, thin film, coating layerfor spectral control and which have enhanced water vapor permeability.

2. Background Information

For the past few decades, flexible solar control sheets have been in useto improve the energy transmission, and appearance of transparentglazing used in commercial buildings, residential buildings andvehicles. This invention relates to solar control sheets that areretro-fitted to already installed transparent glazing surfaces, orlaminated to a glass or other glazing material surface as part of theoriginal assembly of a glazing product. In this second case, a solarcontrol sheet is installed on a transparent glazing surface as part of afenestration manufacturing process before the window is installed in abuilding or vehicle.

The purpose for using these flexible energy control sheets is to alterthe solar energy transmission, reflection, absorption, and emission ofglazing. The most common function is to reduce solar heat gain therebyimproving comfort and reducing cooling load within an architectural ortransportation structure. Some energy control sheets are designed sothat the surface of the sheet facing away from the rigid glazing towhich the sheet is attached has high thermal infrared reflectivity. Suchlow emissivity sheets reduce thermal energy loss through glazing andcontribute to reduction of heating energy requirements when outdoortemperatures are below indoor temperatures in a building or vehicle.Alteration of the visible, and infrared spectral characteristics ofglazing is primarily done with optical thin film coatings. Although manyalternative designs exist, the most commonly used optical thin filmstructures in solar control sheets may be categorized into three basictypes. The simplest sheets reduce light transmission evenly in thevisible and infrared wavelengths. These sheets are not consideredspectrally selective, and usually contain one thin film layer consistingof an optically neutral nickel alloy. The second type of solar controlsheet uses an infrared reflecting metal such as aluminum, copper orsilver as its thin film layer and the reflection level in the infraredwavelengths is increased in these sheets making them somewhat spectrallyselective. The third type of solar control sheet also contains infraredreflecting metals but makes use of thin optical interference layers aswell. The optical interference layers are usually nonabsorbing orslightly absorbing dielectric layers. The interference layersantireflect the metals and result in solar control sheets with highvisible transmission, high infrared reflectance, low visiblereflectance, and low infrared transmission. Some combinations ofinfrared reflecting metals and interference layers result in sheets withhigh spectral selectivity. This invention concerns flexible solarcontrol sheets which contain such thin film layers and are attached to asurface of rigid transparent glazing by an adhesive.

For purposes of optical clarity, solar control sheets must be attachedto the surface of a rigid transparent glazing material such as glasswith no trapped air or other sources of optical distortion. Except incertain manufacturing environments where a sheet can be rolled onto aglass surface with precision equipment, dry adhesive cannot be attachedto dry glass without incorporating air. Particularly when applied toalready installed glazing, proper positioning of a solar control sheeton a glazing surface is a problem due to the tendency for instantaneoussticking of adhesive to glass. The two problems of air entrapment andpositioning are solved by the addition of water or a dilute solution ofwater and surfactant between the solar control sheet's adhesive and theglass surface. With the presence of this aqueous solution acting as alubricant and spacer, positioning of the sheet and subsequent squeezingout of trapped air is relatively easy. Once all positioning and airremoval is complete, squeezing or squeegeeing of residual solution outfrom between solar control sheet and glass is done until as much liquidis removed by this technique as possible. Complete removal of water andsurfactant is not possible by this squeezing process. Some residualsolution always remains between the solar control sheet and the rigidglazing surface.

The result of this water aided attachment process and its leftover layerof aqueous solution is not without negative consequences to the solarcontrol sheet. The water portion of the remaining solution diffuses intothe materials from which the solar control sheet is assembled and, if itremains too long in this assembly, causes undesirable chemical changes.The most immediate change is the formation of a two phase mixture ofwater and adhesive polymer in the adhesive layers that are part of thesolar control sheet assembly. This two phase mixture causes thescattering of visible light which gives the sheet a milky translucentappearance. Solar control sheets applied to glazing and that retainwater for more than approximately six hours will form the mixtures ofadhesive and water. Although not permanent, the initial formation andduration of this milky appearance is dependent on the overall watervapor permeability of the solar control sheet. If water diffuses throughand evaporates from the solar control sheet within a few hours andbefore the mixture of adhesive and water has time to form, the milkyappearance will not occur. Solar control sheets that dry within this fewhour period under ambient conditions that are not unusually cold andhumid (<5° C. and >70% relative humidity), are hereafter referred to as"rapid drying" or "water permeable".

Other problems, as a consequence of the residual, aqueous, surfactantsolution, are corrosion of metal thin film layers within the solarcontrol sheet assembly and optical distortion of the adhesive layer incontact with the rigid glazing surface. Corrosion of the metal layersoccurs from the water contained within the assembly acting as anelectrolyte and causing galvanic chemical activity. The metal layerspresent for spectral control are less than 100 nanometers thick and evensmall amounts of galvanic chemical activity will destroy their intendedoptical function. Optical distortion within the attachment adhesivelayer is cause by coalescence of the residual solution into poolsbetween the adhesive and rigid glazing. These pools appear exactly likewater filled blisters and as long as they are present they distort theoptical clarity of the solar control sheet. Often these blisters, ifpresent for days without drying out, will create permanent deformitiesin the adhesive and subsequent undesirable permanent optical distortionin the solar control sheet. The occurrence of both corrosion of themetal layers and adhesive distortion are related to the overall watervapor permeability of the solar control sheet.

Water vapor permeability of the various components of the solar controlsheet assembly are not equal. The polymer layers within this assemblywhich typically include polyethylene terephthalate sheets or otherpolymer sheets, adhesive layers, and hard polymer layers for abrasionresistance all have sufficient water vapor permeability to avoid thepreviously mentioned problems associated with residual attachmentsolution. If these were the only layers present in the solar controlsheet, residual solution would diffuse through the film rapidly enoughto cause no detrimental effects. Sufficiently rapid diffusion of waterthrough and evaporation away from the sheet until water contentequilibrium is reached with the ambient humidity, hereafter known as"drying", needs to occur within a few hours for none of the problems tooccur, especially for the milky appearance.

The optical thin film layers deposited upon the polymer sheets withinthe solar control sheet assembly, minus some exceptions to be noted, donot share the same degree of water vapor permeability as the polymerlayers. Most vacuum deposited thin film layers typically used forspectral control are excellent barriers to diffusion of water vapor.These thin film layers are the water vapor diffusion rate determiningsegment of a solar control sheet and it is the permeability of theselayers that is the focus of this invention.

Solar control sheets that are water vapor permeable and thereforenon-clouding, non-blistering and less prone to corrosion are morecommercially viable than those that are water impermeable. A large partof the market for solar control sheets is application to automotiveglazing. For safety reasons and to achieve a pleasing appearance, it isimportant for solar control sheets applied to automotive glazing toexhibit no clouding or distortion when they are applied. Waterpermeability related problems causing poor optical clarity of a solarcontrol sheet in the automotive market will severely limit itssalability.

For solar control sheets applied to the architectural glazing market,the water permeability related problems are not a safety hazard as inthe automotive market but will still substantially limit the salability.Distortion and cloudiness lasting more than a day or two are generallyconsidered unacceptable in a solar control sheet applied to residentialor commercial buildings. When solar control sheets are applied toglazing as part of a window manufacturing process, they are usuallyapplied to the one of the internal surfaces of a dual pane insulatingglass unit. Inclusion of water vapor within the internal gas space in aninsulating glass unit will cause condensation formation for the life ofthe unit which is considered unacceptable in the industry. Therefore,before the two glass panes and the gas space are sealed, the solarcontrol sheet must be thoroughly dried. Drying an impermeable solarcontrol sheet is expensive due to the time required and would not besalable to this manufacturing market.

As noted above, solar control sheets which have sufficient waterpermeability for rapid drying are highly desirable in the technologicalfield to which this invention applies. Also noted is the fact that ofall the layers within the solar control sheet assembly, the vacuumdeposited thin film layers are the water permeability limiting portion.It is the physical structure of thin film layers that is the primarydeterminant of the rate at which water may pass through a solar controlsheet. Films formed of tightly compacted atoms or molecules are barriersto water passage. Films that have columnar or crystalline structures andhaving open spaces between columns or crystals are more permeable towater. The physical structure of these thin film layers varies dependingon their deposition method, the materials from which they are formed andtheir thickness.

Vacuum deposition methods by which typical thin film solar controlcoatings are made are either thermal evaporation or direct currentmagnetron sputtering. These deposition processes are distinguished byhow the individual atoms or molecules are separated from the sourcematerial and accelerated towards the substrate. In the process ofthermal evaporation, the source material is heated until atoms ormolecules leave its surface as vapor which recondenses on the substrate.In the sputtering process, kinetic energy of a positively charged ionaccelerated towards the negatively biased source material (thesputtering target) transfers its energy to the atoms or molecules at thesurface of the source material. This transfer of energy results in thechipping off of surface atoms or molecules. An important difference inthese two deposition processes is the kinetic energy they impart to thedepositing atoms and molecules. Atoms and molecules deposited withthermal evaporation carry low levels of kinetic energy (less than 1electron volt) and are more likely to form thin films with openstructures that are water permeable. Solar control sheets containingtransparent layers of thermally evaporated aluminum or nickel are commonand sufficiently water permeable to be considered rapid drying products.

The vacuum deposition method of direct current magnetron sputtering isthe most commonly used process for forming thin film coatings of metalsother than aluminum for solar control sheets and is characterized by thehigher level of kinetic energy it imparts to the depositing atoms (1 to10 electron volts). Depositing metal atoms carrying high kineticenergies are far more likely to form thin film layers with tight compactstructures and are usually insufficiently water permeable to beconsidered fast drying. Neither transparent nickel or aluminum thinfilms are considered rapid drying in a solar control sheet whendeposited by sputtering. The metals of gold, copper and silver and theiralloys which have high infrared reflectivity and are necessary toproduce spectrally selective, high visible transmission, low infraredtransmission solar control sheets are typically deposited by directcurrent magnetron sputtering. They generally do not form water permeablefilms.

The commonly manufactured solar control sheets with neutral gray,nonspectrally selective optical characteristics have relatively similarreflectance and transmission characteristics across all of theultraviolet, visible and infrared spectrum. The thin film metals used toproduce the nonspectrally selective solar control sheets are typicallytitanium, chromium, iron, nickel, niobium, molybdenum, and alloys ofthese. The most common method of depositing these thin film metals forsolar control sheets is direct current magnetron sputtering, and whendeposited by sputtering, they generally are not water permeable.

In some solar control sheet products, it is desirable to achieve greaterspectral selectivity than that exhibited by the neutral grey metallayers described above. Solar control sheets with visible transmissiongreater than 50%, visible reflectance less than 15%, infraredreflectance greater than 50%, and infrared transmission less than 15%are useful in the marketplace due to their potential for improving theenergy efficiency of architectural or automotive windows. The spectralselectivity is typically achieved by alternating thin film layersconsisting of infrared reflecting metals and dielectric opticalinterference layers. The metal layers usually consist of direct currentmagnetron sputtered silver, copper, gold or their alloys. The dielectriclayers may be sputtered or thermally evaporated, and their effect isdesigned to reduce reflectance and raise transmission of the metals inthe visible wavelengths. These multilayer spectrally selective films areparticularly impermeable to water.

Thermal evaporation can be accomplished by a few different methods. Fornonmetallic materials with low vapor pressures such as titanium dioxide,electron beam evaporation is sometimes used. In the electron beamprocess, a beam of electrons is aimed directly at the evaporant held ina high temperature crucible. Temperatures high enough to evaporatevirtually any material can be reached by this technique. When oxides orother compounds are evaporated, the atoms in the molecular structure ofthe compound are often dissociated due to the extreme heat. For example,when TiO₂ is brought up to its vacuum vaporization temperature, some ofthe titanium and oxygen atoms separate and a portion of the releasedoxygen is pumped away by the vacuum pumps. Consequently, the coating isnot stoichiometric TiO₂ but is instead a titanium rich compound which isoptically absorbing. Vacuum coaters typically require clear(non-absorbing) TiO₂ and compensate for the lost gas by adding extraoxygen into the chamber during the coating process. However, in othertechnological fields which provide a metal oxide coating, such as thetechnological field relating to the manufacture of heat mirrors onlenses, glass and small polymer substrates, it is important to carefullycontrol the amount of extra oxygen added during the coating processbecause if too much oxygen is added, the deposited titanium dioxidebecomes porous. Porosity in these other technological fields isundesirable and precautions are used to prevent its occurrence so as tokeep the deposition clear but not porous.

Such porous coatings in these other technological fields have never beenassociated with any method of making a porous metal coating on asubstrate especially a thin film substrate for retrofit application onwindows and consequently no one has ever used such coatings to produce aporosity inducing surface for inducing porosity of materials, such asmetals, which are coated on solar control sheets. This is not surprisingin view of the undesirability of porosity in these other technologicalfields.

As noted above, it is known in other technological fields to make heatmirrors on lenses, glass and small polymer substrates which include athin film structure having the layers TiO₂ /Ag/TiO₂ wherein TiO₂ servesas a dielectric layer. Many other dielectrics are used also for heatmirrors on lenses, glass, and small polymer substrates. Other typicallyused dielectrics include ZnO, ZnS, Nb₂ O₅, SnO₂, Ta₂ O₅, or In₂ O₃.Occasionally the process produces poor quality porous stacks. However,practitioners in these other technological fields never attributed suchporosity with any specific characteristics of a layer upon which anothermaterial is deposited. Thus the undesirable porosity of such a stackcould be attributed to other factors, such as the thickness of thelayers or coating conditions for the metal layer rather than to theselection of physical characteristics of a layer upon which other layersare deposited. In any event, practitioners in these other technologicalfields never regulated the porosity of a primer layer in order toachieve porosity in a subsequently applied metal layer nor would theyfind it desirable to do so. Thus, it was never apparent to suchpractitioners that a porous metal coating could be obtained through theuse of a process which employs a metal coating step conducted underconditions which would normally produce a non-porous coating but for theselection of a primer layer having certain porosity inducingcharacteristics.

Resistance evaporation is another commonly used evaporation technique toprovide a coating on an article. This process is similar to electronbeam evaporation except electric current flowing through a heatingelement is used as the heat source to evaporate the coating material.This process also requires the addition of extra oxygen to the chamberfor the same reasons noted above with respect to the electron beamevaporation coating. Resistive evaporation techniques as used in othertechnological fields typically require careful control of the oxygencontent to keep the deposition clear but not porous. In othertechnological fields, e-beam and resistive evaporation are used forthousands of different types of coatings. Most of these coatings requirecareful control of oxygen to minimize porosity and absorption.Consequently, the same statements discussed above regarding electronbeam evaporative coating are applicable to resistance evaporativecoating techniques.

In other technological fields, porosity is considered detrimental. Forexample, it is known in the glass industry that a reactively sputteredzinc oxide coating can be made by sputtering a zinc target in asputtering gas (e.g. argon) containing sufficient oxygen so that theentire surface of the zinc target is converted to the oxidized state.Under these conditions the properties of the deposited coating changesdramatically since the active portion of the sputtering target, itssurface, is no longer metallic but is the metal oxide. For mostsputtered materials, as the target surface goes from metal to oxide, thecoating also goes from metal to oxide and usually both are relativelyimpermeable to water vapor. For some materials, as the chemicaltransition from metal to oxide occurs, so does the structural transitionfrom non-porous (impermeable to water vapor) to porous. Materials whichare known to follow this pattern are zirconium and zinc.

Metal oxides or other compounds which may be used in solar controlsheets are more complex with regard to thin film structure and waterpermeability characteristics. Metal oxides and other chemical compoundthin films generally follow the same rule of permeable structure asmetals; that is the higher the kinetic energy of the atoms the tighterthe film structure. For metal oxides and other compounds, however, thereare other factors which can dictate whether the thin film structures arewater permeable or impermeable. The most important of these factors isthe makeup and pressure of the background gas as the films are depositedin the vacuum chamber. High background pressures of reactive gas,particularly amounts in excess of that which is required to produce astoichiometric compound will result in thin films with open permeablestructures. In fact, one embodiment of this invention makes use ofexcess amounts of reactive gases such as oxygen to produce thin filmswith specific degrees of openness in their structure.

Table 1 compares the water permeability of optically transparent, thinfilms deposited on a polyethylene terephthalate sheet substrate.

                  TABLE 1                                                         ______________________________________                                        Water Permeable Thin Films                                                                       Water Impermeable Thin Films                               ______________________________________                                        evaporated aluminum                                                                              sputtered aluminum                                         evaporated nickel  sputtered nickel                                                              sputtered silver                                           evaporated oxides  sputtered copper                                           some oxides sputtered in excess oxygen                                                           most reactively sputtered oxides                                              without excess oxygen                                      nickel alloys sputtered in argon                                              pressures between 40 and 60 microns                                           of mercury                                                                    ______________________________________                                    

The water permeability of solar control sheets is measured in terms of awater vapor transmission rate (WVTR). The units of measurement areusually grams/square meter/day. Generally, if the WVTR of a solarcontrol sheet is 2 grams/square meter/day or more, drying time issufficiently short as to avoid cloudiness caused by entrapment of waterbetween the film and the glass. Therefore, solar control sheets whichhave a WVTR of at least 2 grams/square meter/day are considered as beingsufficiently water permeable to be considered rapid drying in thisinvention. Those which have a WVTR less than 2 grams/square meter/dayare considered as being water impermeable in this invention and are notconsidered fast drying. A typical solar control sheet assembly as shownin FIG. 1 consisting of a glazing attachment adhesive, a 12 micron thickUV absorbing polyester (polyethylene terephthalate) sheet, a laminatingadhesive, a 25 micron polyester sheet, and a 1 micron acrylic abrasionresistant coating but no thin film layers to limit water permeability,have a WVTR of approximately 20 grams/square meter/day. The same solarcontrol sheet assembly described above but containing vacuum depositedthin film layers may have a WVTR from 0.1 to 20 grams/square meter/day.The thin film layers in solar control sheet assemblies are the componentthat determines whether a sheet is to be rapid drying or not.

Conventional devices known to those skilled in the art may be used tomeasure the water permeability of a solar control sheet. One such deviceused to measure permeability, commonly referred to as a "mocon", iscommercially available from Modern Controls Inc., 6820 Shingle CreekParkway, Minneapolis, Minn. 55430. The water vapor transmission ratesdescribed in relation to this invention are obtained by operating theinstrument in accordance with ASTM test procedure F372-73 (reapproved1984).sup.δ2. The instrument uses a removable diffusion cell havingupper and lower halves. In operation, test samples of a sheet are cutinto pieces about 4 inches by 4 inches (10 cm×10 cm). The sample sheetis mounted between the upper and lower halves of a removable diffusioncell so as to form a divider between two enclosed chambers (upper andlower halves). The lower volume of the assembled cell block containspads moistened with distilled water or saturated salt solution (NaCl).The upper volume is vented through two openings that permit a constantflow of dry air to pass across one side of the film. The mating internalsurfaces of the diffusion cell define an area of 50 square centimeters.

The test sheet mounted in the diffusion cell is clamped into the testchamber. When inserted, the sheet is exposed to a continuous flow of dryair across the upper side while the bottom side is exposed to watervapor from the moistened pads in the humid cavity. Gas leaving the drycavity via the exhaust port consist of a mixture of air and water vaporin a ratio determined by the dry air purge rate and the rate of moisturetransmission through the sheet barrier. Thus, it can be easilyunderstood that if the flow rate of dry air into the cell is maintainedat some arbitrary constant value, the resulting water vapor density inthe exhaust line will be determined by the sheet water vaportransmission rate.

The water vapor concentration of the diffusion cell exhaust flow ismonitored by an infrared detector. Over the concentration range ofinterest, the detector output displayed by the digital meter is a linearfunction of the transmission rate of moisture through the sheet.

Three approaches are available for overcoming the above noted cloudingproblem of solar control sheets in this technological field. In oneapproach, the use of water in the mounting process could be eliminated.However, the water serves to promote slip during the mounting process sothat the film can be readily positioned on the window, and the waterserves to facilitate the removal of trapped air bubbles. Thus, use ofthe water to solve the clouding problem will create extreme applicationdifficulties. At this time there is no known way to apply solar controlsheets to existing glazing without the use of an aqueous solution.

Another approach could involve using non-clouding adhesives. Thistechnology is presently practiced in the industry by some participantsto reduce the clouding problem. However, this does not solve the otherproblems of corrosion of the metal thin film layers and opticaldistortion associated with long term entrapment of water. Thus,elimination of the non-clouding adhesives would not solve all theproblems associated with the use of water as a mounting media.

Another approach involves substituting impermeable, thin film, opticallayers with permeable layers which have the requisite permeability sothat the water can rapidly diffuse through the film. As noted above, thenumber of permeable thin film layers is limited. Solar control sheetsthat are the most spectrally selective and exhibiting the most desirableoptical properties generally make use of silver, copper, or gold metallayers. These metals cannot be made permeable through standarddeposition techniques practiced today.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a porous solar controlsheet which includes porous structured thin film layers therein havingsufficient permeability for the transmission of water vapor therethroughso that when the film is mounted on rigid glazing with a water basedmounting media, residual water which is left between the film and therigid glazing can readily escape by diffusion or transmission throughthe layers of the sheet.

It is a further object of this invention to provide a method for makinga multiple layered solar control sheet having one or more porous watervapor transmissible thin film layers as a component thereof. The thinfilm layers are porous for the transmission of water vapor therethrougheven though the thin film layers are deposited under conditions whichwould normally produce a water impermeable (non-water vaportransmissible) thin film layer. No special modifications to the thinfilm deposition process is necessary to achieve the desired permeabilityof the thin film layers and residual water left between the film and theglass can be dissipated by evaporation through the multi-layered solarcontrol film.

It is a further object of this invention to provide a method of makingporous copper, silver, and other infrared reflecting metal thin filmcoatings for a solar control sheet. It is a further object of thisinvention to provide a method of mounting a solar control film on awindow with a water based mounting media while eliminating the formationof cloudiness, corrosion and distortion associated with water whichbecomes trapped between the film and the glass during the mountingprocedure.

These and other objectives are accomplished by providing the polymersheet substrate with a porosity inducing surface whereby the porosityinducing surface induces porosity in one or more layers sequentiallydeposited thereon. A porosity inducing surface may be formed byproviding the polymer sheet with a porous primer layer having a porositycharacteristic which permits vacuum deposition of a water permeable thinfilm layer or layers on the porous primer under coating conditions whichwould normally produce a water impermeable thin film if the coating wereapplied on a substrate which lacks the porous structure of the primerlayer. In other words, the porous primer layer itself is selected forspecific porosity characteristics so that no special porosity promotingor permeability promoting coating conditions are required for subsequentthin film layers which would normally be impermeable. Thus, permeablethin film layers can be deposited under conditions which would otherwiseresult in a water impermeable thin film but for the porous structurecharacteristics of the primer layer. A porous primer coating may causeone or more subsequent thin film layers to be water permeable. Theporosity inducing surface may also be formed by providing the polymersheet substrate with a roughened surface. Such a porosity inducingsurface will induce porosity in a coating deposited thereon like theporosity inducing surface associated with a porous primer layer.

Although the primer layer must be porous to cause the subsequentlyapplied thin film layers to become permeable, not all porous materialswill cause subsequently applied layers to be permeable. Some materials,such as the typical polyethylene terephthalate sheets which are used asthe substrate for thin film layers in conventional solar control sheets,are known to be water permeable, but the porous structure is notadequate to transfer to the subsequently applied thin film layers andcause them to also be permeable. Similarly, some vacuum deposited layerssuch as sputtered nickel alloys which are deposited under conditionswhich make the metal coating water permeable (water vapor transmissible)lack the required porosity characteristics which are necessary to causea subsequently applied thin film layer to be permeable. Thus the porousprimer layer must have a sufficient porosity to cause normallyimpermeable thin film layers to be permeable when sputtered thereon. Inthe case of oxides such as SiO₂ and SnO₂, which are the preferredprimers, an adequate level of porosity may be achieved by usingbackground oxygen during the evaporative deposition. It has beenobserved that as the oxygen level increases, so does porosity of a thinfilm oxide. For example, it has been determined that using an oxygenpartial pressure of 3 microns of mercury and 5 microns of mercury isadequate to achieve the required porosity for reactively evaporated SnO₂and SiO₂ respectively and that increasing the amount of backgroundoxygen beyond this amount will result in greater porosity.

In general, the pore size of a deposited primer layer should be greaterthan 1 nm in diameter. Pores larger than about 100 nm should be avoidedbecause such large size pores will cause scattering of visible lightresulting in a hazy appearance. This range of desirable pore size, 1 to100 nanometers, also applies to layers deposited onto the porous primerthat have porosity induced by the porous primer. Pore sizes aredetermined by surface analysis techniques such as scanning electronmicroscopy or transmission electron microscopy.

It has been observed that sputtered gold, silver, copper, palladium ortheir alloys will be porous when deposited onto a porous primer layer ofZnO. Preferably, the ZnO has a thickness of at least 2 nm when it hasbeen deposited by reactive sputtering from a zinc metal target. Inaddition, when the ZnO is deposited in this manner, it is preferable toconduct the sputtering with excess background oxygen to enhance theporosity of the primer layer. Preferably an oxygen pressure of at least25% to 50% over the amount needed to produce clear ZnO is used toprovide the background oxygen during the reactive sputtering of the zincmetal target. ZnO deposited in this manner will be porous due to thecolumnar physical structure of the coating.

Stainless steels or nickel alloys will be porous when deposited onto aporous primer layer of ZrO₂. Preferably, the ZrO₂ has a thickness of atleast 30 nm when it has been deposited by reactive sputtering from a Zrmetal target. In addition, when the ZrO₂ is deposited in this manner, itis preferable to conduct the sputtering in the presence of backgroundoxygen to enhance the porosity of the primer layer. Preferably, anoxygen partial pressure of at least 50% over the level needed to produceclear ZrO₂ is used to provide the background oxygen. ZrO₂ deposited inthis manner is porous due to its columnar structure.

Almost any semi-transparent metal or compound layer including gold,silver, copper, palladium, nickel, iron, chromium, titanium, molybdenum,aluminum and alloys or multiple layers of these materials will be porouswhen deposited on a porous primer layer of SnO₂. Preferably, the SnO₂has a thickness of at least 30 nm when it has been deposited by reactiveevaporation of SnO₂. In addition, when the SnO₂ is deposited in thismanner, it is preferable to conduct the reactive evaporation in thepresence of background oxygen to enhance the porosity of the primerlayer. Preferably, an oxygen partial pressure of 3 microns of mercury isused to provide the background oxygen. SnO₂ deposited in this manner isporous due to its columnar structure.

Stainless steels, nickel alloys and titanium will be porous whendeposited onto a porous primer layer of SiO₂. Preferably, the SiO₂ has athickness of 30 nm when it has been deposited by reactive evaporation ofSiO. In addition, when the SiO₂ is deposited in this manner, it ispreferable to conduct the reactive evaporation with background oxygen toenhance the porosity of the primer layer. Preferably, an oxygen partialpressure of 5 microns of mercury is used to provide the backgroundoxygen. SiO₂ deposited in this manner is porous due to its columnarstructure.

Instead of using the primer layer formed by the reactive evaporation ofSiO, it is possible to obtain a suitable porous primer layer by applyinga coating of SiO₂ sol gel to the desired substrate. Such a porous primerlayer will have a sponge like porosity. Nickel alloy sputtered onto sucha SiO₂ sol gel primer layer will have adequate porosity for thisinvention.

It has been observed that sputtered gold will be porous when depositedupon a polycarbonate substrate wherein the surface of the polycarbonatehas been etched. The polycarbonate may be etched by any known procedurewhich creates a roughened or porosity inducing surface.

It has been observed that sputtered silver will be porous when depositedupon a porous primer layer of TiO₂. Preferably, the TiO₂ is deposited byreactive electron beam evaporation. Like the oxides described above, theTiO₂ primer layer may be deposited in the presence of background oxygenin order to enhance the porosity of the primer layer. TiO₂ deposited inthis manner will be porous due to its columnar structure. For example, asuitable partial pressure of oxygen is 0.2 microns of mercury in orderto form a porous TiO₂ primer layer. Sputter coating a layer of silver onsuch a porous TiO₂ primer layer results in the silver layer being waterpermeable. Sputtering this same layer of silver on a non-poroussubstrate will not result in the formation of a water permeable silverlayer. The above procedure was used to form a 12 nm water permeablesilver layer on top of a 40 nm layer of porous TiO₂.

The thin film layers such as the metals used in this invention may bemade from any of the materials which are conventionally used in thefield of solar control films. Thus, the alloys mentioned in thisspecification such as the nickel alloys used in some of the embodimentsdescribed herein may be the same as the nickel alloys which areconventionally used in solar control film technology. Preferred nickelalloys are Hastelloy C 276 and Inconel 600.

Hastelloy C 276 has the following mechanical properties: UTI tensil psi:106,000; yield psi: 43,000; elong % 71.0. Hastelloy C 276 has thefollowing chemical analysis:

    ______________________________________                                        HASTELLOY C 276                                                                      element                                                                             % by weight                                                      ______________________________________                                               C     .004                                                                    Fe    5.31                                                                    Mo    15.42                                                                   Mn    0.48                                                                    Co    1.70                                                                    Cr    15.40                                                                   Si    .02                                                                     S     .004                                                                    P     .005                                                                    W     3.39                                                                    V     0.16                                                                    Ni    Balance                                                          ______________________________________                                    

Inconel 600 has the following mechanical properties: UTI tensil psi:139,500; yield psi 60,900; elong % 44.0; hardness: Rb85. Inconel 600 hasthe following chemical analysis:

    ______________________________________                                        INCONEL 600                                                                   element       % by weight                                                     ______________________________________                                               C      .08                                                                    Fe     8.38                                                                   Ti     0.25                                                                   Mn     0.21                                                                   Cu     0.20                                                                   Co     0.05                                                                   Cr     15.71                                                                  Si     0.30                                                                   S      <.001                                                                  Al     0.28                                                                   P      0.01                                                                   Ni     74.45                                                                  Nb + Ta                                                                              0.08                                                            ______________________________________                                    

The coatings are applied to films through the use of conventional filmcoating devices. Such a device is shown in FIG. 8. FIG. 8 showsschematically a vacuum roll coating apparatus 20. Apparatus 20 containsa chilled support drum 21 which carries a polyethylene terephthalatesheet in roll form 22. Uncoated sheet is supplied from pay-roll 23 andcoated sheet is re-wound onto take-up 24. Subchamber shields 25 separatedeposition sources 26, 27 and 28. Deposition sources 26 and 28 are DCmagnetron sputtering sources and source 27 is a resistively heated boxevaporation source with source material 29. Gas inlets 30 and 32 feedargon to the sputtering sources and gas inlet 31 feeds oxygen to theevaporation source. Gas exits through vacuum outlet 33.

A conventional resistively heated box evaporation source may be used fordepositing the porous primer layer. A conventional resistively heatedbox evaporation source is shown in FIG.9. The box is heated by passingelectric current through the graphite box lid 34 and the graphite sideheaters 39. Insulator 35 electrically isolates lid 34 from the graphitebox 36. The box 36 contains the evaporant source material 40. Thermalinsulating material 37 and water cooled outer shell 38 prevent lost heatfrom heating surrounding vacuum chamber walls. Source material vapor 41is deposited on polymer sheet substrate 42 carried by cooled drum 43.Gas inlet 44 supplies oxygen background gas. Conventional evaporationsources may be used and such sources may be purchased from LeyboldTechnologies, Enfield, Conn. or from Galileo Vacuum Systems, EastGranby, Conn.

The possible variations of material choices and deposition methods ofporous primer layers are numerous. In its simplest application, a thinfilm structure requiring improved permeability may consist of only onelayer, and the porous primer layer serves no other purpose than to makethis single layer permeable. In this case, the single layer is usually ametal, and any suitable porous primer material may be chosen. It isknown that not all combinations of primers and metals areinterchangeable. DC magnetron sputtered nickel alloys can be madepermeable by a layer of porous reactively evaporated SiO₂ while copperor silver metal layers do not become permeable when sputtered over thisprimer. The difference in response to a porous primer from one metaltype to another is related to the physical properties and physicalstructure of the porous primer and metal layers.

This porous primer invention includes any layer or surface serving anypurpose within a solar control thin film structure as long as it is alsoused to cause a desirable increase in water permeability of a thin filmstructure deposited on that layer or surface. Porous primer layers oftenserve only the one function to cause subsequent thin film layers to bepermeable, but porous primers may also serve dual functions within theoptical thin film structure. For example, a porous primer layer may alsofunction as an optical interference layer, a corrosion protection layer,or a physical adhesion enhancement layer. Secondary optical functionsfor a porous primer layer are likely since porous primers often have thesame optical properties as optical interference layers. It is onlynecessary to set the porous primer thickness to a specific level for itto serve some of the typical uses of an optical interference layer. Theporous primer may serve to function for such purposes as anantireflection layer for a metal, the resonant cavity dielectric in aFabry-Perot structure, or to alter the reflection or transmission colorof a thin film structure. A porous primer may also be used to induceporosity in an interference layer which would normally not be permeable.In this instance, the primer may or may not contribute an optical effectdepending on its index of refraction. Certain porous primer layers havebeen found to cause the metal layer not only to be permeable but to bemore corrosion resistant. Adhesion between layers of a thin filmstructure also becomes greater when a porous primer is present. Thesurface area of attachment of adjacent thin film layers and between thinfilm layers and laminating adhesives of the solar control sheet assemblyis greater when the structures are porous.

A porous primer may be deposited from a variety of different methods andformed from a variety of different materials. The preferred method ofdeposition is with vacuum processes similar to that used to depositother thin films within the solar control thin film structure. Thesedeposition processes are typically reactive thermal evaporation ordirect current magnetron sputtering. The thermal processes aredistinguished by their heat sources and are typically either reactive,electron beam evaporation or reactive, resistively heated evaporation.Maximum evaporant temperatures achievable with resistance heating areless than the temperatures which can be achieved with electron beamevaporation. Consequently, resistance evaporation techniques forproducing the porous primer layer are limited to materials which can beevaporated by the temperatures achievable by means of resistanceheating. Evaporatable compounds which can be deposited by resistanceevaporation include oxides or other compounds of aluminum, silicon,zinc, indium, tin, tungsten, bismuth, antimony, cerium, magnesiummolybdenum and barium. Oxide mixtures or oxide compounds containing morethan one metal may also be effective in creating a porosity inducingsurface.

Most porous primers are formed oxides from a reactive depositionprocess. Stoichiometric oxides or other compounds may also be referredto as fully oxidized or fully reacted compounds. A reactive depositionprocess is one where the reactive gas, oxygen in the case of oxides, ispresent in the vacuum chamber during the deposition process. Thedepositing atoms and molecules from the sputtering target plate or theheated evaporant source material undergo chemical oxidation as they aredeposited and with increasing oxygen pressure, become increasinglyporous.

Many types of vacuum deposition processes such as those described aboveand others, can be used to make a porous primer layer. Other types ofnonvacuum porous primer layers are also possible. For example, sol gelcoatings can be used to form a porous primer layer. Porous primer layersmay also be obtainable through the use of water based polymer coatings.The polymer particle suspensions in water (often referred to as latex)emulsions may form the necessary porous primer structure the porosity ofwhich can be regulated by coating at specific dilution levels which areknown to those skilled in the art. Suitable polymers for this type oflatex coating may include styrene butadiene, acrylic, and polyurethane.Porous primer layers may also be obtained from filled polymer coatings.Polymeric organic layers containing sufficient amounts of particlefillers are known to have porous structures.

Inorganic/organic composites may also be used to form the porous primerlayers. Such coatings are coated as mixtures of inorganic and organiccompounds or organic molecules with inorganic functionalities attached.The resulting coatings are chemical composite structures which mayexhibit controllable porosity. Plasma deposited inorganic or organiccoatings can also be used to form a porous primer layer. For example,porous oxides or other compounds may be deposited by passing anorganometallic or silane chemical through an atmospheric or reducedpressure plasma. Partial disassociation of these molecules by theenergetic plasma leaves them in a sufficiently reactive state that theywill attach themselves to a substrate. It is known that the porosity ofsuch coatings can be controlled depending on the deposition processparameters utilized.

The present invention is particularly suitable for making solar controlfilms which are capable of functioning as heat mirrors ("heat mirror" isa registered trademark of Southwall Corp.). In particular, the inventioncan be used to make a solar control film which includes TiO₂ /Ag/TiO₂ asa stack on a water permeable polyester substrate. In this embodiment thefirst layer of TiO₂ which is in contact with the substrate functions asa porous primer layer. In addition, this first TiO₂ layer has an opticalfunction as part of the heat mirror stack. The silver layer is sputtercoated on top of the first TiO₂ layer and the silver is rendered waterpermeable because of the porosity of the TiO₂ primer layer. The outerTiO₂ layer which is optically functional in the heat mirror stack (TiO₂/Ag/TiO2) may be coated in the same way that the first TiO₂ layer iscoated so that it is also porous. Thus, if an additional metal is coatedon the exposed surface of the second or outer TiO₂ layer, then thisouter layer will function as porous primer layer to cause the additionallayer coating to be water permeable. All of the metal layers in thisheat mirror solar control film are water permeable so that water vaporcan pass therethrough.

The following examples illustrate specific embodiments of the inventionwhich have been tested. Sputtered zirconium oxide is used to make anichrome alloy layer porous in the structure having the layers polyesterfilm/ZrO₂ (30 nm)/sputtered nichrome alloy. Silicon dioxide from a solgel coating process is used in the structure having the layers:polyester film/sol gel SiO₂ /nichrome alloy. Similarly, electron beam,vacuum evaporated titanium dioxide was used to make silver porous in thestructure containing the layers: polyethylene terephthalate sheet/TiO₂/Ag/TiO₂.

The useful thickness of a porous primer layer covers a wide range anddepends on the primer material and the material of the layers caused tobe permeable. Porous primer layer thickness may be as low as 1 nanometeras has been found in the case of zinc oxide to several microns in thecase of porous polymer coatings. If the porous primer has a secondaryfunction such as an optical interference layer, the exact thicknesswould be determined by the optical function rather than its permeabilityfunction.

It is also possible to alter the surface of a polymer substrate toproduce controlled porous surface topology capable of causing normallyimpermeable thin films to be permeable. Plasma or chemical etching of apolymer surface may be used to create the proper porous structure.Subsequently vacuum deposited layers will be porous when they areapplied to the surface of a polymer substrate which has beensufficiently roughened in this manner. For example, chemically etchedpolycarbonate film causes a subsequently applied layer of sputtered goldto have the required water permeability. Preferably, the surface shouldbe roughened so that material deposited thereon will have a columnarstructure. Roughened surfaces which induce columnar growth are describedin the publication "Effect of Substrate Roughness on the Columnar Growthof Cu Films" by P. Bai, J. F. McDonald and T. M. Lu, J. Vac. Sci.Technol. A 9(4), July/August 1991; the text of which is incorporatedherein by reference.

Specific coating methods have been described herein as appropriatetechniques for forming the porous primer layer. However, the porousprimer layer which is formed or deposited on the substrate film does nothave to be formed by such coating processes if the surface of thesubstrate layer can be modified so as to form a porous layer thereon. Inother words, the porous primer layer on the substrate can be formed bysimply subjecting the surface of the substrate to an etching procedure(e.g., chemical or plasma etching) to form an integral layer having therequired porosity characteristic. For the purpose of the presentinvention, such a modified surface is considered as a porous primercoating or layer on the substrate. Thus, the porous primer coating maybe an adherent layer deposited on the substrate by the methodsheretofore described or alternatively the porous primer layer may be anintegral porous layer formed by modifying the surface of the substrate.In either case the substrate has a porous surface topography so thesubsequently deposited thin film layer is rendered water permeable.

The solar control sheets of the present invention may besemi-transparent, spectrally selective or even opaque. Asemi-transparent sheet allows only a portion of the light to passtherethrough. A spectrally selective sheet will substantially preventpassage of a particular wavelength or range of wavelengths and willalloy other wavelengths to pass through the sheet. Typically, suchspectrally selective sheets will allow passage of the visible light butnot allow passage of the infrared and/or ultra-violet light. Opaquesheets substantially block the passage of visible light as well asinfrared and ultra-violet light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the sequence of layers found in conventional prior artsolar control film.

FIG. 2 depicts the sequence of layers found in an alternative embodimentof a conventional prior art solar control film which provides a loweremissivity surface.

FIG. 3 shows the cross-sectional layers found in a stack of layers ofthe present invention in its simplest embodiment.

FIG. 4 illustrates an alternative embodiment of a stack of layers madein accordance with the present invention with reduced reflection andneutral color transmission.

FIG. 5 illustrates an embodiment of the invention with high visiblelight transmission and high infrared reflection.

FIG. 6 illustrates an embodiment of the invention with an infraredreflecting metal surrounded by thin protective layers.

FIG. 7 illustrates an embodiment of this invention which is a modifiedversion of the sheet shown in FIG. 5. FIG. 7 shows the addition of asecond metal/dielectric thin film pair which gives the sheet greaterspectral selectivity.

FIG. 8 shows schematically a vacuum roll coating apparatus with threedeposition subchambers.

FIG. 9 shows schematically a cross section drawing of a resistivelyheated, box evaporation, deposition source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This porous primer invention applies to any thin film coating orsubstrate surface topology within a flexible solar control sheetassembly that causes optical thin film layers to be water permeable thatwould otherwise be impermeable. The increased water permeability theporous primer causes in the solar control sheet must be sufficient toraise the water vapor transmission rate of the solar control sheet to atleast 2 grams/square meter/day. At this level of permeability or higher,the solar control sheet is considered fast drying and problems ofclouding, corrosion, and adhesive distortion are eliminated or reduced.Layers within the thin film structure requiring improved permeabilitymay be metals, metal alloys, metal oxides, or other chemical compoundsin thin film form or combinations of any of these layers. A porousprimer may cause one or more of these normally non-permeable layers tobe permeable. In some multilayer thin film structures, more than oneporous primer layer may be required to cause the entire thin filmstructure to be permeable.

A typical prior art solar control sheet assembly containing thin filmlayers is shown in FIG. 1 with the layer configuration as follows:

Layer 1.--One micron thick acrylic polymer abrasion resistance layerapplied by solvent coating.

Layer 2.--Twenty three micron thick polyethylene terephthalate sheetwhich serves as a substrate for the thin film layers.

Layer 6.--Vacuum deposited thin film layers which in the simplest solarcontrol sheet assemblies typically consists of one transparent layer ofnickel alloy or aluminum. More complex multilayer thin film structuresmay be used to achieve particular spectral characteristics in a solarcontrol sheet.

Layer 3.--Polymeric adhesive which adheres layers 1, 2, and 6 to layers4 and 5.

Layer 4.--Twelve micron thick polyethylene terephthalate sheetcontaining compounds to absorb ultraviolet light at wavelengths from 320nanometers to 380 nanometers.

Layer 5.--Polymeric adhesive used to attach the solar control sheetassembly to the surface of a rigid glazing material which is usuallyglass.

The reference numerals 1-6 identified above for FIG. 1 are used toidentify corresponding layers in FIGS. 2-7.

FIG. 2 shows a solar control sheet modified to increase the thermalinfrared reflectivity (lower emissivity) of one surface of the sheet. Toincrease the reflectivity at the thermal wavelengths of 8 to 12 microns,the layer 6 is an infrared reflecting metal layer which is positionedbetween layers 1 and 2. The polyethylene terephthalate polymer of layer2 is absorbing at the wavelengths of 8 to 12 microns which absorbs theinfrared energy before it reaches the metal layer 6. The modified solarcontrol assembly of FIG. 2 positions the metal layer to a locationwithin the assembly where its infrared reflective qualities are notblocked by a polyethylene terephthalate polymer sheet. The acrylicpolymer of layer 1 is also absorbing in the thermal infrared, but iflimited to a thickness of 1 micron or less the infrared absorption issufficiently minimized. The acrylic polymer layer 1 may be replaced bythermal infrared transparent polymers such as polyethylene orpolypropylene described in U.S. Pat. No. 4,226,910, the specification ofwhich is included herein by reference. In the configuration of FIG. 2,layer 6 usually consists of an infrared reflecting metal such asaluminum or a multilayer thin film structure containing silver, copper,or gold.

Preferred embodiments of this invention include the following examples.

EXAMPLE 1

In the simplest embodiment of this invention the porous primer layerwould have the sole function to cause one subsequently deposited thinfilm layer to become water permeable. A common version of a prior artsolar control sheet used in both automotive and architecturalapplications as depicted in FIG. 1 is with one 15 nanometer metal layer6 deposited on polymer layer 2 wherein the metal layer is HastelloyC-276 which is chosen for its visually appealing neutral transmissionand reflectance color as well as corrosion resistance. The nickel alloyis deposited by direct current magnetron sputtering with 2 microns ofmercury argon background pressure. When the solar control sheet is fullyassembled as shown in FIG. 1, its visual light transmission is 30%.Water permeability of the prior art solar control sheet product shown inFIG. 1 is not sufficient for the sheet to be considered fast drying. Tomake the sheet fast drying, a porous primer shown as layer 7 in FIG. 3consisting of porous SiO₂ is deposited on polymer layer 2 prior to thenickel alloy shown as layer 6. When the nickel alloy is subsequentlydeposited on the porous SiO₂, the nickel alloy is caused to haveincreased water permeability. The porous SiO₂ is deposited from aconventional resistively heated graphite box evaporation source as shownin FIG. 9. The source material in the graphite box is SiO and is heatedto 1150° C. to 1250° C. The vapor is deposited as porous SiO₂ by addingoxygen as a background gas in the vacuum chamber during the depositionprocess. The oxygen partial pressure in the deposition chamber ismaintained at 8 microns of mercury. A porous SiO2 thickness of 30nanometers is sufficient to cause the nickel alloy to be permeable. Thispolyethylene terephthalate sheet with its thin film coatings is thentransferred to solvent coating and lamination processes where the fullsolar control sheet assembly as shown in FIG. 3 is completed.

EXAMPLE 2

Solar control sheets containing nickel alloy layers with visible lighttransmission levels of 30% have visible light reflectance levels greaterthan 20%. Reflectance levels greater than 20%, especially on theinterior side of a window, are undesirable in some retro-fit solarcontrol markets. The SiO₂ porous primer layer described in example 1 mayserve a dual use if the thickness of the SiO₂ is such that it functionsas an optical interference, antireflection layer as well as a primercausing the subsequent layer of nickel alloy to become water permeable.If the SiO₂ is between 70 and 200 nanometers thick, preferably about 110nanometers, it will reduce the visible wavelength reflectance of thenickel alloy on the SiO₂ side. Reduced reflectance levels on one side ofa solar control sheet between 5% and 20%, which this antireflectionlayer provides, are often desirable in the solar control sheet market.

EXAMPLE 3

The same two layer structure described in example 2 and depicted inFIG.3 may be modified into a more spectrally selective, infraredreflecting coating by substituting the nickel alloy with silver. SnO₂deposited from a resistively heated box evaporation source is thepreferred porous primer for silver, copper, gold, and their alloys. Todeposit this primer layer, SnO₂ source material is placed in thegraphite box and thermally evaporated. When the SnO₂ is heated totemperatures of 1150° to 1250° Centigrade, the compound partiallydissociates and some of the released oxygen is pumped away by the vacuumchamber's pumping system. To compensate for the lost oxygen, oxygen isadded as a background gas during the deposition process. To form a layerof SnO₂ with the proper structure for it to function as a porous primerfor a subsequent infrared reflecting metal layer, the background oxygenpressure is maintained at 5 microns of mercury. SnO₂ deposited withoxygen background pressures below 5 microns tends to be opticallyabsorbing and does not cause subsequently deposited metal layers to bewater permeable. SnO₂ deposited with background oxygen pressures above 5microns tends to form a powdery coating with poor adherence to thepolyethylene terephthalate substrate. The SnO₂ primer layer is 30nanometers thick to cause the subsequent infrared reflecting metal to bewater permeable. The subsequent metal layer is deposited by directcurrent magnetron sputtering and my be from 5 nanometer to 40 nanometerthick depending on the optical characteristics desired in the solarcontrol sheet.

EXAMPLE 4

An alternative primer layer which may be used to cause an infraredreflecting metal become water permeable when the metal is sputterdeposited over the primer is zinc oxide. When ZnO is used as the primerLayer subsequent to the deposition of the infrared reflecting metallayer, it is deposited by reactive, direct current, magnetronsputtering. In this process the pure zinc metal is the magnetron cathodematerial and the sputtering background gas consists of a mixture ofargon and oxygen. As the sputtering of zinc is carried out, the degreeof oxidation of the depositing film of zinc oxide is controlled by theoxygen to argon gas ratio. In conventional ZnO Sputtering, as is used inthe glass coating industry for coating multilayer, low emissivity glasscoatings, the oxygen level is typically raised no further than todeposit nonabsorbing, stoichiometric ZnO. It is normally undesirable toraise the oxygen level higher since it causes the ZnO to become moreporous and the deposition rate decreases. For the purposes of thisinvention where the ZnO is used to cause subsequently deposited layer tobe porous, the oxygen to argon ratio is intentionally raised 50% higherthan is necessary to achieve stoichiometric ZnO. The ZnO primer is 3nanometers thick to cause subsequent layers to be water permeable.

EXAMPLE 5

Very thin protective layers may be added to one or sides of an infraredreflecting metal to improve color, appearance or corrosion resistance.In FIG. 6, the infrared metal is shown by layer 15 and the protectivelayer on either side of it by layer 14 and 16. The practice of usingthin protecting layers is common on transparent layers of silver andcopper which are prone to corrosion when contained in a solar controlsheet. These protective layers may be as thin as a few atomic layers andusually do not exceed 4 nanometers thick. They may be chosen from manydifferent materials, Nickel, chromium, molybdenum, palladium, gold,titanium, zirconium or alloys of these metals are typical choices. Metaloxides, nitrides, carbides or other thin film compounds are also used asprotective layers. Infrared reflecting metals with protective layersgenerally are not water permeable and used of porous primer is the onlyway of achieving permeability in magnetron sputtered layers of thesemetals. The thin film structure shown in FIG. 6 is formed by sequentialdeposition of four thin film layers. The primer layer of SnO₂ isdeposited from a graphic box evaporation source with a source materialof SnO₂ heated to its vaporization of 1150° to 1250° Centigrade. Abackground pressure of oxygen is maintained at 5 microns of mercury. TheSnO₂ primer layer, layer 17, is coated to a thickness of 60 nanometersand serves the additional optical function of antireflecting the metallayers on the interior side of the solar control sheet. The firstprotective layer is nickel deposited by direct current magnetronsputtering to a thickness of 2 nanometers. The infrared metal,consisting of silver is sputter deposited to a thickness of 20nanometers. Finally the second protective layer is deposited similarlyto the first protective layer. The SnO₂ primer layer induces waterpermeability and reduces visible light reflection on one side of allthree metal layers.

EXAMPLE 6

FIG. 4 shows a solar control sheet typically used for automotiveapplications with a Fabry-Perot type 3 layer thin film structure ofmetal/dielectric/metal. Hastelloy C-276 is used as the two metal layersand SiO₂ as the center dielectric, and this structure provides aneutral, visible, transmission color with reflectance levels on bothsides of the solar control sheet of about 7%. Reflectance levels createdby this three layer structure for a given transmission level are lowerthan if a single metal layer of nickel alloy is used. Glazingreflectance below levels of less than 10%, which this design provides,are desirable for automotive applications in the solar control industry.In this embodiment, each nickel alloy layer which may consist of Inconel600 or Hastelloy C-276 as shown in FIG. 4 by layer 8 and layer 10 mayrange in thickness from 2 nanometers to 15 nanometers. The opticaltransmission desired in the solar control sheet dictates the thicknessesused. The optical interference layer between the two metal layers asshown by layer 9 in FIG. 4 in this embodiment is porous SiO₂ and is 120nanometers thick.

If no technology is used to induce porosity in this 3 layer thin filmstructure, resulting water permeability of the solar control sheet istoo low for the sheet to dry rapidly. When the porous primer technologyof this invention is applied, the water permeability of the solarcontrol sheet may be raised almost to the level of a solar control sheetincorporating no thin film layers. In this three layer thin filmstructure, the porous SiO2 layer is deposited under conditions so thatit causes the subsequently deposited metal layer 10 to become waterpermeable even though it is deposited under conditions which normallywould not cause it to be permeable. Metal layer 8 in FIG. 4 is madepermeable by sputtering it in an argon background gas pressure of 40microns.

EXAMPLE 7

It is often desirable in the field of solar control for a glazing tohave the optical properties of high visible light transmission and highinfrared reflectance; both being in the range of 60% to 90%. Thin filmlayers which may be used to accomplish this spectral selectivity areshown in FIG. 5. Layer 11 is a nonabsorbing dielectric whichantireflects metal layer 12. Layer 13, like layer 11, is also anonabsorbing dielectric. Layer 13 functions to antireflect the metal onthe opposite side. The metal layer 12 is usually silver, silver alloy ora silver layer with very thin metal protective layers on one or bothsides of the silver metal. The latter two versions of metal layer 12,silver alloy and protected silver metal, are modifications to reducecorrosion of the silver. The metal layer 12 may also consist of otherheat reflecting metals such as Cu, Au, Ni, or Al or their alloys.Conventional versions of layers 11 and 13 are typically reactivelymagnetron sputtered or thermally evaporated oxides of metals Ce, Sn, In,Zn, Ti, Nb, Mo, Ta, W or combinations of these oxides. Conventionalversions of this heat reflecting thin film structure are usuallyinsufficiently permeable to allow a solar control sheet to be fastdrying. The silver layer within conventional versions of this thin filmstructure is particularly impermeable to water. Unlike Inconel 600 andHastelloy C 276, silver and copper thin films which are the most usefulof the heat reflecting metals cannot be made permeable by sputteringwith a background argon pressure of 40 to 60 microns of mercury.

The heat reflecting thin film structure shown in FIG. 7 may be modifiedin accordance with this invention to produce a water permeable solarcontrol sheet. In accordance with this invention, the first dielectriclayer 11 coated onto polymer layer 2 is a porous layer of evaporatedSnO₂ which functions as a porous primer and optical interference layer.Maximum permeability can be obtained if the second SnO₂ dielectric layer13 is also deposited to be porous, although, this may not be necessaryto make the solar control sheet fast drying.

This SnO₂ primer used in the heat reflecting thin film structure shownin FIG. 7 is 60 nanometers thick and is deposited by thermal evaporationof SnO₂ from a resistively heated graphite box evaporation source. SnO₂is the source material placed in the box and thermally evaporated. Whenthe SnO₂ is heated to evaporation temperatures of 1150° C. the compoundpartially dissociates and some of the released oxygen is pumped away bythe vacuum chamber's pumping system. To compensate for the lost oxygen,oxygen is added as a background gas during the deposition process. Toform a layer of SnO₂ with the proper structure for it to function as aporous primer for subsequent silver layers, the oxygen pressure ismaintained at 5 microns of mercury. SnO₂ deposited with oxygenbackground pressures below 5 microns tends to be optically absorbing andinsufficiently porous to function as a porous primer layer. SnO₂deposited with background oxygen pressures above 5 microns tend to bepowdery and poorly attached to the substrate. The infrared reflectingmetal layers are deposited by direct current magnetron sputtering andmay be from 5 nanometers to 30 nanometers thick depending on the opticalcharacteristics desired in the solar control sheet. The heat reflectingmetal layer 12 is deposited by direct current magnetron sputtering. Thethickness is 12 nanometers. Layer 13 is evaporated SnO₂ deposited by thesame process as layer 11 to a thickness of 60 nanometers.

More layer pairs of metal/dielectric may be added over layer 13 of thisthin film structure to increase the spectral selectivity. Where theseadditional layers are added, each dielectric deposited prior to a metalmust be of a porous primer in accordance with this invention for thesolar control sheet to be fast drying. FIG. 7 shows a solar controlsheet assembly containing a five layer spectrally selective thin filmstructure. Layers 11, 12, and 13 in FIG. 7 are the same as shown in FIG.5. Layer 19 in FIG. 7 is an additional layer of sputtered infraredreflecting metal and layer 18 is an additional layer of evaporated SnO₂.

EXAMPLE 8

Silver/porous quarter wave thickness spacer layer/copper (this is aFabry-Perot structure that produces a good quality solar control sheetdue to its spectral selectivity). The quarter wave thickness opticalspacer is resistively evaporated and may be clear or slightly absorbing.The preferred spacer material is evaporated SnO₂. The center layer inthis embodiment functions as a porous primer to the second metal andalso functions as an optical interference layer. The layer structure inthis design is the same basic metal/dielectric/metal design as depictedin FIG. 4. Design variations for this embodiment include:

porous primer/silver/optical spacer/copper (for porosity in the firstmetal layer);

protective layer/silver/optical spacer/copper/protective metal (forcorrosion protection); and

silver/optical spacer/copper/optical spacer/silver (an extra oxide/metalpair for enhanced spectral selectivity).

A porous primer layer formed of WO₃ may be formed by the same procedureused to form a porous primer layer of SnO₂.

The term "oxide" is meant to include a single oxide as well as a mixtureor combination of oxides. Thus a primer layer which comprises an oxideincludes primer layers made from a single oxide or a mixture of oxides.

The term "metal" which is not qualified as a "metal compound" or "metaloxide" means that the metal is in the elemental state and includesalloys of metals.

While the present invention has been described in terms of certainpreferred embodiments, one skilled in the art will readily appreciatethat various modifications, changes, omissions and substitutions may bemade without departing from the spirit thereof. It is intended,therefore, that the present invention be limited solely by the scope ofthe following claims.

What is claimed is:
 1. A method for making a water vapor transmissiblesolar control sheet of the type which comprises a water vaportransmissible film with a light affecting coating thereon; said lightaffecting coating including a metal layer or a metal compound layer;wherein said method comprises forming a porosity inducing surface on awater vapor transmissible film and then depositing a metal or metalcompound coating on said porosity inducing surface to induce theporosity of said coating as said coating is deposited on said porosityinducing surface whereby said coating is rendered porous for thetransmission of water vapor therethrough.
 2. The method of claim 1wherein the porosity inducing surface is produced by coating said watervapor transmissible film with a primer layer which has said porosityinducing surface on an exposed surface thereof.
 3. The method of claim 2wherein the primer layer is a vacuum coated layer deposited by coatingunder a vacuum.
 4. The method of claim 3 wherein the primer layer has athickness of about 2 nm to 200 nm.
 5. The method of claim 4 wherein thevacuum coated primer layer is deposited by vacuum sputtering.
 6. Themethod of claim 5 wherein the vacuum coated primer layer has a thicknessof 2 nm-120 nm.
 7. The method of claim 6 wherein the primer layercomprises oxide.
 8. The method of claim 6 wherein the vacuum sputteringis reactive sputtering.
 9. The method of claim 6 wherein the solarcontrol sheet formed by said method has a water vapor transmission rateof at least 2 gm/sq. m./day.
 10. The method of claim 4 wherein thevacuum coated primer layer is deposited by evaporation under a vacuum.11. The method of claim 10 wherein the primer layer has a thickness ofabout 10 nm to 200 nm.
 12. The method of claim 11 wherein the vacuumcoated primer layer comprises oxide.
 13. The method of claim 11 whereinthe evaporation is reactive evaporation.
 14. The method of claim 11wherein the solar control sheet formed by said method has a water vaportransmission rate of at least 2 gm/sq. m./day.
 15. The method of claim 5wherein the sputtering process is reactive and the reactive gas partialpressure is greater than 2 microns of mercury.
 16. The method of claim 8wherein said primer layer has an optical interference property wherebysaid primer layer functions as an optical interference layer as well asa layer which contains a porosity inducing surface.
 17. The method ofclaim 16 which includes forming a stack on said metal or metal compoundcoating; said stack comprising a combination of at least one additionalprimer layer and at least one additional metal or a metal compound layerwherein said at least one additional primer layer has said porosityinducing surface to induce porosity in said at least one metal or metalcompound layers in said stack.
 18. The method of claim 17 wherein saidstack forms a multi-layer optical coating which includes a dielectricporosity inducing layer, porous dielectric layer rendered porous by saiddielectric porosity inducing layer and a porous metal or porous metalcompound layer.
 19. The method of claim 2 wherein said primer layercontains pores which form said porosity inducing surface; said poresranging in size from 1 nm-100 nm.
 20. The method of claim 2 wherein apressure of at least one atmosphere is maintained during the coatingprocess.
 21. The method of claim 20 wherein the coating is applied to athickness of 30 nm to 3 microns.
 22. The method of claim 21 wherein thecoating is a porous organic layer.
 23. The method of claim 21 whereinthe organic layer is a porous organic polymeric coating.
 24. The methodof claim 21 wherein the coating is an organic/inorganic composite. 25.The method of claim 24 wherein the organic component of said compositeis a polymer.
 26. The method of claim 25 wherein the composite is apolymer filled with inorganic particles.
 27. The method of claim 24wherein the solar control sheet formed by said method has a water vaportransmission rate of at least 2 gm/sq. sq./day.
 28. The method of claim21 wherein the primer layer is deposited by applying a sol-gel coatingon said film.
 29. The method of claim 28 wherein the sol-gel is a SiO₂sol-gel.
 30. The method of claim 1 wherein the coating which is renderedporous has pores which are 1 nm-100 nm in diameter.
 31. The method ofclaim 1 wherein the coating which is rendered porous is sputter coatedonto the porosity inducing surface to achieve a coating thickness of 5nm-40 nm.
 32. The method of claim 31 wherein the solar control sheetformed by said method has a water vapor transmission rate of at least 2gm/sq. m./day.
 33. The method of claim 1 wherein metal is deposited onsaid porosity inducing surface so that said coating which is renderedporous is metal.
 34. The method of claim 33 wherein the metal isselected from the group consisting of silver, copper, gold and alloysthereof and said metal coating is applied to achieve a coating thicknessof about 5 nm to about 40 nm.
 35. The method of claim 34 wherein themetal is an alloy containing at least 50% by weight of Ag, Cu or Au. 36.The method of claim 34 wherein the metal coating which has been renderedporous is silver or an alloy thereof whereby said silver or silver alloyhas a porosity inducing surface for inducing porosity in a subsequentlyapplied coating and said method further includes sequentially depositingadditional metal or metal compound coatings onto said silver or silveralloy coating to form a stack of elemental metal or metal compoundcoatings on said silver or silver alloy coating and wherein eachsequentially applied coating is rendered porous with a porosity inducingsurface whereby each porosity inducing surface induces porosity in thenext sequentially applied coating so that the stack is porous for thetransmission of water vapor therethrough.
 37. The method of claim 33wherein the metal coating which is rendered porous is a semi-transparentmetal having a neutral colored transmission and a neutral coloredreflection from either surface of said metal coating.
 38. The method ofclaim 37 wherein the metal coating which is rendered porous is titanium,stainless steel, or nickel alloy.
 39. The method of claim 1 wherein saidmetal or metal compound coating deposited on said porosity inducingsurface is formed by depositing a first coating on said porosityinducing surface and then depositing a second coating on said firstcoating wherein said first coating is selected from the group consistingof metal, metal alloy, metal compound and combination of metal and metalcompound and said second coating is a metal or metal alloy, with theproviso that said first and second coatings are different.
 40. Themethod of claim 39 which further includes depositing a third coating onsaid second coating; said third coating selected from the groupconsisting of metal, metal alloy, metal compound and combination ofmetal and metal compound, with the proviso that said second and thirdcoatings are different.
 41. The method of claim 40 wherein the secondlayer is silver and the first and third layers are metal or metal alloy.42. The method of claim 1 wherein the metal or metal compound coatingdeposited on said porosity inducing surface is formed by depositing afirst coating on said porosity inducing surface and then depositing asecond coating on said first coating wherein said first coating is ametal or metal alloy and said second coating is selected from the groupconsisting of metal, metal alloy, metal compound or combination of metaland metal compound, with the proviso that said first and second coatingsare different.
 43. The method of claim 1 wherein the porosity inducingsurface is formed by roughening the surface of said water vaportransmissible film.
 44. The method of claim 43 wherein the surface isroughened by chemical etching.
 45. The method of claim 44 wherein thesurface is roughened by plasma etching.